The colour of unbleached linen (4)
I believe the answer is:
ecru
'the colour of unbleached linen' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ecru that I've seen before include "Buff or beige" , "Natural stuff" , "Strange cure for a colour" , "one of the colours" , "No bright colour" .)